Error on using a11y with ME.js

[ManuelTS]

With ME.js v 4.2.16, 4.2.13, and 4.2.12 and the a11y plugin, I get the following error:

mediaelement.js:4821 error building a11y TypeError: sources.find is not a function
    at MediaElementPlayer._evaluateBestMatchingSource (a11y.js:184)
    at MediaElementPlayer._loadSourceFromAttribute (a11y.js:155)
    at MediaElementPlayer.builda11y (a11y.js:66)
    at MediaElementPlayer.buildfeatures (mediaelement.js:4819)
    at MediaElementPlayer._meReady (mediaelement.js:4048)
    at Object.success (mediaelement.js:3709)
    at new MediaElement (mediaelement.js:990)
    at MediaElementPlayer.init (mediaelement.js:3826)
    at new MediaElementPlayer (mediaelement.js:3693)
    at HTMLVideoElement.<anonymous> (mediaelement.js:5523)

so I guess it is on the a11y side. The scripts are in the same folder and are aware of each other, the video and audio tags are found and their respective callbacks are called. Versions:

Manuels-MBP:website manuel$ gulp -v
CLI version: 2.3.0
Local version: 4.0.2
Manuels-MBP:website manuel$ npm -v
6.14.4
Manuels-MBP:website manuel$ node -v
v13.13.0

The tags of the video contain the attributes of a11y, and the last one isdata-audio-description-voiceover="false".